Shipboard Measurement of Ocean Waves

Over the past several years a number of techniques have been utilized for the measurement of ocean waves from shipboard platforms. These systems have ranged from commercial off the shelf (COTS) navigation radar and Light Detection and Ranging (LIDAR) systems to specially developed in-house instrumentation systems. Most of these systems have been utilized to measure the directional wave spectra around the ship. More recently, the Naval Surface Warfare Center, Carderock Division (NSWCCD) and others have begun to utilize these techniques for shipboard measurement of individual ship generated waves as well as open ocean waves. NSWCCD has used a number of these methods on various Office of Naval Research (ONR) and Naval Sea Systems (NAVSEA) sponsored field tests. These field tests were performed on a variety of naval platforms over a range of sizes, including some fixed platforms, for various sea states. While each of these tests has had individual measurement goals and objectives, the series of tests has also provided an environment for testing and developing new instrumentation and exploring their capabilities. As a result of these efforts, instrumentation has grown in sophistication from qualitative video-based observations of the wave field around an underway vessel to laser and radar based imaging and ranging measurements of free surface dynamics. This work has led to higher fidelity data, as well as data that were previously unobtainable. In this paper we provide an overview of these systems and techniques and summarize the basic capabilities of each method by providing measurement examples/applications. These systems include a shipboard array of ultrasonic distance sensors for measuring directional wave spectra, a COTS wave radar system, and a COTS scanning LIDAR system. While not intending to be exhaustive, this paper seeks to highlight the insights gained from the recent applications of these techniques, as well as the difficulties and issues associated with shipboard measurements such as ship motion and logistical constraints.